TFBs comprise a “stack” of two, one negative (“anode”) and one positive (“cathode”) thin-film active material electrode layers (referred to henceforth simply as “electrodes”) separated by an ionically conducting and electronically insulating (“non-conducting”) separator layer. Hereinafter, the various battery layers are mentioned without use of the word “layer”. The thickness of each electrode may range from sub-micrometer (“sub-micron”) to a few microns. The thickness of the separator may range from sub-micron to a few tens of microns. The stack is formed on a substrate. If one or both electrodes are not sufficiently electronically conductive, thin film current collectors (“CC”s) are provided to facilitate electron current flow in an external circuit. One such CC is formed on the substrate prior to the formation of the TFB stack.
3D-TFBs, as disclosed for example in U.S. Pat. No. 6,197,450 to Nathan et al., are formed inside perforations (through-holes or cavities) of a substrate as well as on any remaining original (planar) surface of the substrate. Each perforation may include a partial or full stack of concentric layers forming a “concentric microbattery” or “CMB”. Such 3D-TFBs combine the known advantages of 2D-TFBs with an order of magnitude and more increase in power and energy per footprint (original substrate area). A general known problem with CMBs is the difficulty of forming a solid separator using wet chemistry. Also, known art does not teach electrochemical deposition of a full three layer battery stack.
“Electrophoresis” refers to the motion of charged particles in a liquid under an applied electric field. Electrophoresis can be used to deposit materials in the form of thin films (layers), coatings and bulk products. The deposition process is commonly termed “electrophoretic deposition” (EPD). Reviews of EPD include those by Van der Biest and Vandeperre, Ann. Rev. Mater. Sci., 29 (1999) 327-352 and by Corni et al., J. Europ. Ceram. Soc., 28 (2008) 1353-1367. The EPD of layers faces a hurdle in the requirement that the solid to be deposited be available as a colloidal suspension or powder with grains smaller that a required layer thickness.
EPD has been used to produce bulk battery electrodes, see e.g., Kanamura et al., Electrochemical and Solid-State Letters, 3 (2000) 259-262, and Kanamura et al., J. Power Sources, 97-98 (2001) 294-297. The use of EPD to prepare film (thick or thin) battery components has been extremely limited, and applied mainly to positive electrodes (cathodes). Structures and materials investigated include thick films of LiNi0.5Mn1.5O4 [Caballero et al., J. Power Sources 158 (2005) 583-590] and relatively thin films of Li4Ti5O12 [Sugiura et al., Functional Mater. Lett. 2(1) (2009) 9-12]. A general concern and trend in the EPD of TFB electrodes it to make them dense (as opposed to porous).
Electrophoretic assembly of electrochemical devices is also disclosed by Chiang et al. in U.S. Pat. No. 7,662,265. Their methods requite always use of two current collectors (“terminals”) for EPD of mutually repulsive electrodes, and cannot be used to EPD TFBs on a single current collector.